1. Field of the Invention
The present invention relates to electronic-component conveying devices for conveying multiple electronic components which are arranged at a predetermined pitch. In particular, an electronic-component conveying device according to the present invention is suitable for inspection devices which measure electrical properties of electronic components for sorting out defective components from non-defective components.
2. Description of the Related Art
FIGS. 5 and 6 illustrate a conventional inspection device, such as the one disclosed in U.S. Pat. No. 5,842,579, which measures electrical properties of electronic components to sort out defective components from non-defective components. Such a device is provided with a conveying plate 20 having multiple component-holders 20a arranged in three lines. The holders 20a in each line are arranged at a predetermined pitch along a conveying direction α of the conveying plate 20. The device is further provided with component-containers 21, 22, and 23 which are respectively disposed above conveying paths A, B, and C, i.e. the three lines, of the conveying plate 20. The containers 21, 22, and 23 hold electronic components W. Each electronic component W is supplied to one of the component-holders 20a. The conveying plate 20 is rotated intermittently so as to convey the components W to an electrical-property inspection unit, not shown in the drawings, of the subsequent step.
To allow continuous processing of the electronic components W, the containers 21, 22, and 23 are respectively provided with level sensors 24, 25, and 26. When the components W in one of the containers 21, 22, and 23 decrease and therefore cannot be detected by the corresponding one of the level sensors 24 to 26, additional electronic components W are fed to the component-container. The feeding of the components W is stopped at the point in which these additional components W are detected.
In an inspection device of this type, when the feeding of the electronic components W is aborted to switch to another production lot, for example, if there are components W remaining in the containers 21 to 23 at this aborting point, the device carries on with its operation until the inspection for the remaining components W is completed.
In such a conventional inspection device, however, the electronic components W are fed when the detected containing level of the components W in each component-container falls below a certain level. Even if a certain problem occurs in one of the containers 21 to 23 and the components W are not supplied to the conveying plate 20, the device will continue its operation regardless of the state in which one of the conveying paths of the conveying plate 20 may have empty component-holders. Accordingly, this may lower the operational efficiency.
Furthermore, as described above, from the aborting time of the feeding of the electronic components W, such a conventional inspection device continues its operation until the inspection for all remaining components W in the containers 21 to 23 is completed. For this reason, if there are differences in the number of components W among the containers 21 to 23, the device must continue the operation in a state where some of the conveying paths may have empty component-holders. This may lower the rate of operation. Referring to FIG. 5, for example, the container 21 in the left side of the drawing contains a small number of electronic components W, the container 22 in the center does not contain any components W, and the container 23 in the right side contains a large number of components W. Consequently, even though the processing efficiency is lowered to ⅓, the device must continue the operation. In a case where a conveying plate having two conveying paths is rotated intermittently at 0.1 second per tact, if there is a difference of 10,000 electronic components between the two component-containers of the conveying paths before switching to another production lot, the device must continue the operation for approximately 17 more minutes while the processing efficiency is lowered to ½.
Such a conventional inspection device detects the containing level of the electronic components in each component-container. As a result, if each electronic component has an extremely small size of, for example, 0.6 mm by 0.3 mm by 0.3 mm, a 1-cm3 capacity would contain approximately 10,000 electronic components. Accordingly, when the detected objects are small in size, the detection may become difficult unless a certain number of the objects are present. As a result, the electronic components in each container must be large in number.